The Tapered Stem

 

Cementless fixation in total hip arthroplasty emerged as a result of the perceived need for more durable longterm fixation. Cementless stems have yielded variable results depending on surgical technique, implant, and patient population. Results with tapered stems, however, appear reproducible and require fewer surgical steps (1,2). This surgical simplicity produces more predictable results. Ten-year results in a number of patient groups seem to indicate that the technique is more versatile than is cemented stem fixation (1,3,4,5,6). Recent study with 20 to 25 years of follow-up also yielded excellent results (7). In addition, the use of second-generation stems in younger patients has also been recently shown to result in positive results (8). While cemented total hip arthroplasty continues to have its advocates, it has been largely replaced by cementless technique using a taper stem in North America. Initial experiences with cementless fixation yielded results that were marred by a number of problems such as femoral fracture, subsidence, thigh pain, and stress shielding. Many of these problems associated with early cementless femoral components have been since addressed (9,10). Currently, cementless femoral fixation with a tapered prosthesis is a straightforward and reliable alternative to more technically demanding cemented femoral fixation.

 

 

INDICATIONS/CONTRAINDICATIONS

The tapered stem is ideally suited to provide fixation in femora with a broad spectrum of bone stock, bone quality, and underlying patient biology. Dorr types A and B femora have been considered the best bone types for cementless fixation. Initially, cementless fixation was thought unsuitable for the patients with Dorr type C proximal femora (such as in patients with rheumatoid arthritis and osteoporosis). The Dorr type C osteoporotic femur has an increased risk of intraoperative femoral fracture. Additionally, a larger stiffer implant is required to produce primary stability, which can result in thigh pain and greater stress shielding especially when cobalt chrome implants are utilized. Experience and published results have shown this not to be as common with a tapered titanium implants (6,7). Currently, successful results are possible in Dorr type C bone with tapered titanium stems. Of course, if there is any concern about the stability of initial fixation, then a cemented implant should be utilized. There have also been some concerns about cementless fixation in type A femora, where the traditional cementless prosthesis might engage distally and toggle loose proximally when the patient mobilizes. Design changes in cementless stems that focus on metaphysical fixation to facilitate more anatomical load transfer and reduce distal diaphyseal fixation seem to have addressed this particular femoral morphology (11).

 

PREOPERATIVE PLANNING

Preoperative templating should determine the appropriate center of rotation of the hip and femoral neck resection level (Fig. 16-1). This can assure reproducible results (12). Both standard acetate templates and computer templating software can be used. AP view of the pelvis centered over the sacrum is used with legs in 15 degrees of internal rotation to provide en face view of the anteverted femoral necks and allow correct evaluation of the femoral offset. Radiographic preoperative leg length discrepancy (LLD) is measured. Templating should follow typical surgical sequence: cup first and then the femur. The cup is placed at the level of the teardrop with

approximately 40 degrees of abduction and medialization

 

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to the ilioischial line. The size is determined by adequate lateral coverage without removal of excess subchondral

bone. Special consideration may have to be undertaken for protrusio acetabuli and dysplastic hips. If the contralateral hip is not affected by disease, templating can be performed on the contralateral side. The goal of templating of the femur is to predict the implant of appropriate size for the femoral canal, to predict the neck cut length, and to restore femoral offset and equalize the limb length. Leg length is reestablished by placing the center of rotation of the femoral head above the center of rotation of the acetabular component for a shortened limb and below the center of acetabular component for a limb that needs to be shortened. The vertical distance between the two centers of rotation is the numerical correction of LLD in millimeters. These measurements, of course, are approximations that must be confirmed intraoperatively. The horizontal distance between these two centers on medial to lateral axis signifies the increase or decrease in femoral offset after the surgery. Standard or higher offset stems can be then used as needed based on radiographic evaluation. In general, templating should estimate and record the following parameters: preoperative LLD, length of the neck cut, estimated sizes of the femoral and acetabular components, and estimated femoral offset.

 

 

 

FIGURE 16-1 Careful templating offers a guide to femoral and acetabular sizing, and it can predict if a stem with a standard or high offset should be used.

 

Multiple studies have shown that well-performed templating can predict LLD correction in more than 90% of patients based on the preoperative plan and that in majority of patients, LLD will be less than 1 cm (13,14,15). The most common errors in execution of a template are lengthening due to inferior cup positioning and increased offset due to inadequate medialization (16).

 

Design Rationale

The double-tapered design is ideally suited to permit fixation within the proximal femur and to provide immediate axial and rotational stability. Cadaver studies by Sharkey et al. (17) have demonstrated that initial axial and rotational stability following implantation of a tapered stem was comparable to that of a cemented prosthesis.

Should initial stability be insufficient for bone ingrowth, the component will subside. Unlike some alternative designs, subsidence of a tapered stem may reestablish implant stability within the proximal femur, providing again the environment for bony ingrowth. The disadvantage is that the restoration of leg length and stability might be compromised. Hence, only small amounts of subsidence should be tolerated.

The wide variation in proximal femoral anatomy and concerns about creating an excessively stiff prosthesis are a further advantage of the tapered stem. A tapered titanium stem provides a progressive transition from bulky and relatively inflexible proximal segment to the narrower and more flexible distal section. This, in turn, permits the loading of the proximal femur and theoretically protects against the effects of stress shielding. Redesign of the tapered femoral components, focusing on proximal metaphyseal fixation and minimization of diaphyseal engagement, also has proven to reduce stress shielding (11).

 

Tapered stems work best without a collar. While a collared prosthesis has the theoretical benefits of providing absolute axial stability and loading the calcar, thus preventing stress shielding, a collar

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also has several significant drawbacks. First, if there is failure of initial stability, then subsidence will be

prevented, and stability cannot be restored. Slight undersizing of the component or a high neck cut might create

this scenario. Second, if component removal is required for any reason, then direct access to the bone-prosthesis interface can be obscured by the collar. Third, for a collar to function with a stable component, there must be a very precise relationship between neck resection level, component design, and the complex three-dimensional anatomy of the proximal femur. This increases the complexity of the surgery unnecessarily. Finally, the collar may prevent full “seating,” creating an axially stable prosthesis without rotational stability.

 

 

 

FIGURE 16-2 Examples of taper stems.

Circumferential proximal porous coating is the current standard. Limiting the porous surface to the proximal area

permits bone ingrowth only in the proximal femur—this promotes loading of the metaphyseal bone and minimizes stress shielding. In addition, should the prosthesis require removal, a more extensive femoral osteotomy is usually not required since the bonded area of the prosthesis can often be accessed from the top. A circumferential proximal coating has the important effect of creating a seal, separating any debris generated by the bearing surface from gaining access to the bone-prosthesis interface, and inducing femoral osteolysis.

The majority of currently available components permit a degree of modularity in terms of neck length. Additionally, it is desirable to have components with more than one offset, which allows the surgeon to better reestablish the proper mechanics of the replaced hip joint—thus insuring good ROM, good stability, and equal leg lengths. The examples of various tempered stems from a variety of companies are presented in Figure 16-2.

SURGERY

Patient Positioning

 

The authors perform all primary and most simple total hip arthroplasty revisions through a direct anterior approach, with patients in the supine position on a standard orthopedic OR table. Supine positioning in this manner permits more accurate assessment of leg lengths intraoperatively as the influence of pelvic obliquity is removed.

 

Surgical Technique

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The incision starts approximately 2 cm distal and 2 cm lateral to the anterior superior iliac spine and extends up to 10 cm toward the lateral aspect of the knee in line with the tensor fascia lata (TFL). The tensor fascia is incised with cautery, and tensor is swept laterally off its posteromedial fascia. The superior neck is identified by palpation, and a blunt Hohmann retractor is placed on the superior neck. A sharp Hohmann retractor is placed on the lateral aspect of the greater trochanter retracting TFL laterally. Another retractor pulls the sartorius medially. These three retractors expose the branches of the lateral circumflex femoral artery, which is carefully cauterized and transected. The remainder of the posterior TFL fascia is incised to expose anterior hip capsule. The inferior femoral neck is identified, and a blunt Hohmann is placed on its surface making sure to place it proximal and not distal. A space between the capsule and a rectus muscle is developed with a Cobb, and a sharp Hohmann with a light source is placed into this space on the anterior column. At this point, the anterior capsule is excised, a double osteotomy of the femoral neck is performed, and the femoral head is removed. The acetabulum is now exposed with three retractors. First, a narrow sharp Hohmann is placed on the posterior acetabulum. Second, the retractor over the anterior column is repositioned directly on bone. Finally, a blunt Hohmann is placed into the teardrop through an incision in the inferior capsule. Standard preparation of the acetabulum is then undertaken with insertion of a cementless hemispherical acetabular component and a crosslinked polyethylene bearing.

Femoral exposure is then begun. The contralateral limb is abducted, and ipsilateral limb is placed in a figure of four position. Retractors are placed laterally and medially to expose the osteotomized femoral neck. A triangular-shaped part of the capsule between the abductors and the posterosuperior acetabulum is identified and excised. Next, the superior capsule is incised down to the inner aspect of the greater trochanter in line with the lateral aspect of the femoral neck cut. The two-prong retractor is now placed into the space created and over the tip of the greater trochanter. A vertical capsular release is now performed in line with this retractor down to femoral neck then curving medially toward piriformis fossa. Piriformis release is usually not necessary. A bone hook is placed into the femoral neck, and the femur is gently raised over and above the posterior acetabular rim. This move should not require much force. The leg is now positioned in adduction and external rotation to allow access to the femoral canal. Femoral retractors are repositioned as needed. The neck cut should be checked and can be revised if required. The importance of sufficient exposure of the femur and deliverance of the femur from under posterior acetabular rim into the incision cannot be understated (Fig. 16-3). While using a tapered stem,

easy access to the femoral canal will allow correct performance of the steps of tapered stem insertion as outlined in the next paragraph. Inadequate femoral exposure can lead to increased risk of calcar fractures, canal perforation, varus positioning of the stem within the canal, and increased damage to the tensor muscle and proximal aspect of the wound.

 

 

 

FIGURE 16-3 Adequate delivery of the proximal femur into the wound exposes entry point to the femoral canal and can make subsequent steps in insertion of the tapered stem significantly less difficult. Before releases and delivery (A). After releases and delivery (B).

 

 

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Tapered Stem Preparation and Insertion

Insertion of the tapered stem follows a precise sequence of steps in order to avoid common intraoperative complications and errors. First, once the proximal femur is exposed, the remnant of the lateral femoral neck

should be removed using box osteotome or large, angled rongeurs/nibblers (Fig. 16-4). This removes a small amount of bone at the base of the piriformis fossa that might otherwise divert the path of the broaching and subsequently force the stem into varus.

 

Next, we usually open the canal and find its direction with a curved, blunt-ended curette (Fig. 16-5). If different surgical approach is utilized, canal finder designed for this purpose or a starting reamer can be used. Great care must be taken not to perforate the femoral cortex, particularly in patients

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with obesity, osteoporosis, or femoral deformity. In anterior approach, a posterior perforation is most common. Third, sequential broaches are employed to contour the femur in both mediolateral (ML) and AP dimensions (Fig. 16-6). It is extremely important that the broaches follow the same trajectory as the initial path of the curved curette. Fewer repeated blows with the mallet and frequent backstrokes with occasional rest help to prevent femoral fracture by relieving hoop stresses of the bone. Malleting technique should ensure that broaching proceeds forward with some force directed lateral to aid lateralization of the broach and avoidance of varus positioning of the stem. Some surgeons use specially designed first lateralizing broach or a lateralizing reamer.

Anteversion should be kept constant and carefully controlled throughout femoral preparation. Altering anteversion after femoral broaching might compromise rotational stability of the definitive implant. Broaching proceeds until a final broach is reached, which often can be quite precisely predicted by templating. There are

 

several clues that help the surgeon determine that the final size of the broach has been reached. First, this broach will be firmly seated on the medial neck bone cut, and once this position is reached (visual clue), there will be an audible change in the pitch of the sound that accompanies the broaching to a higher, sharper metallic pitch (audible clue). Secondly, gentle malleting at this point will not result in advancement of the broach (second visual clue). Applying torsional force to the broach handle at this point should result in no rotational movement of the broach (third visual

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clue). The surgeon should be vigilant to all of these clues, as proceeding with vigorous malleting at this point may lead to a fracture.

 

 

 

FIGURE 16-4 Box osteotome can be used to remove the remnant of the lateral neck cortex and aid in femoral stem lateralization avoiding varus stem placement.

 

 

 

FIGURE 16-5 The direction of the femoral canal can be determined with a blunt curette as shown here or with canal finding reamer.

 

 

 

FIGURE 16-6 Broaching starts with the smallest broach on a double offset broach handle (A). Broaching proceeds with sequentially larger broaches until a final broach is inserted (B). The final broach advancement proceeds until malleting sound changes and the broach is fully inserted and seated securely on the medial femoral neck cortex. Subsequent gentle malleting does not advance the broach any further. Rotational stability is assessed by applying torsional force to the broach handle. No broach movement should be observed (C).

 

 

Next, a broach with a standard neck is first employed unless preoperative templating determines otherwise (Fig. 16-7). Trial reduction with the broach and a standard neck segment follows. Stability is assessed in adduction external rotation, in abduction external rotation, and in flexion external and internal rotation (Fig. 16-8A-C). For anterior approach to the hip, testing in adduction and

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external rotation is most important to prevent anterior dislocation. With reference to the preoperative radiographs and intraoperative assessment, it can be determined whether offset or length is required to produce satisfactory

soft tissue tension and stability. At this point, assessment of leg lengths is performed using the patient's medial malleoli as reference points (Fig. 16-8D). It is important to make sure that the lower extremities are aligned with patient's torso, as abduction and adduction will result in change in apparent leg lengths.

 

 

 

FIGURE 16-7 Trialing proceeds using the neck with previously templated offset and trial head. It is important to remember that final prosthesis is slightly larger and will likely be prouder than the broach.

 

 

 

FIGURE 16-8 Stability is assessed in abduction and external rotation (A), in adduction external rotation (B), and in flexion internal rotation (C). Leg lengths are assessed (D).

 

Once stability and leg lengths are assessed and are found to be satisfactory, the hip is dislocated, the broach is removed, and an implant prostheses is introduced to the canal by hand (Fig. 16-9A). It is gently placed in the space created by the broaching. The use of the stem inserter may increase the risk of fracture because stem

inserter can hit against the greater trochanter or be pushed anteriorly by the proximal aspect of the wound and force the stem into the varus, resulting in a fracture. Stem inserter is used to impact the stem into place once the stem is partially advanced by hand (Fig. 16-9B). Once again, short repeated taps, occasional rests to reduce hoop stresses, and listening for a change in the pitch are employed. If the prosthesis fails to advance to the distance similar to the broach, it should be removed as it is likely placed in a position different to the final broach. Attempt at forceful advancement will likely result in a fracture. Since the final prosthesis is larger than the same size broach due to the applied porous coating, it will usually advance about 2 mm less than the final broach. It is important to make sure to avoid using shortest neck trial on the broach. It is important to leave a possibility to shorten the neck of the final component if that final component turns out to be more proud than the final broach.

Following definitive prosthesis insertion and the trial head in place, a further assessment of leg lengths and stability is made. Following lavage, the interior of the acetabulum should be carefully inspected for debris. The trunnion is carefully cleaned and dried to avoid any debris left on the trunnion when final head is impacted. This may lead to the trunnion corrosion in the future. The definitive head is applied onto the clean trunnion, and reduction is undertaken.

The wound is irrigated and tensor fascia is closed using continuous stitch, making sure to take small bites medially to protect lateral cutaneous nerve of the thigh, which runs just medial to the fascial incision. This is followed by layered closure of the subcutaneous tissue, including scarpa's fascia if present, dermis, and finally running subcuticular closure. Dermabond is applied to the skin followed by waterproof dressing once Dermabond is dry.

 

 

 

FIGURE 16-9 Prosthesis is inserted by hand making sure to follow previously established space in the canal and maintain broached anterversion (A). Inserter is used once the broach is inserted to the two-thirds of its length into the canal (B). Initial use of the inserter can lead to varus placement of the prosthesis and increased risk of calcar fracture.

 

 

 

POSTOPERATIVE MANAGEMENT

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We permit all patients to fully weight bear immediately following their operation; however, we advise the use of crutches, walker, or a cane for up to 4 weeks to guard against falls (18). Most patients will be able to ambulate without assistive devises within 2 weeks after surgery. Younger, healthy patients can be discharged home on the

day of surgery if they meet physical therapy criteria. Most patients will be able to go home the next day. Formal physical therapy is not required.

 

COMPLICATIONS

A three-tiered approach should be employed involving prevention, recognition, and management of intraoperative femoral failure. Prevention requires recognition of those at risk with osteoporotic, deformed, or “tight” femora. Broaching should be careful and controlled in both force and direction. The surgeon should also be aware of the change in pitch during broaching or implantation that may accompany a femoral split. Up to 50% of femoral fractures go unrecognized at the time of surgery (19). Where there are concerns that fracture may have occurred, the surgeon must extend the approach to inspect the femur directly.

Intraoperative radiographs are unreliable in detecting these fractures. If detected intraoperatively, most can be managed with a cable or double wire to close the split (20,21). It is our practice to remove the prosthesis, place a cable closing the split, and then reinsert the prosthesis until the split opens prior to final tightening of the cable. If any doubt exists regarding the primary stability of the construct, then an alternative prosthesis should be employed (20). The stem should bypass the fracture by two femoral diameters. A reasonable alternative might be a fully coated and distally fixed stem (22).

 

 

REFERENCES

1. Teloken MA, Bissett G, Hozack WJ, et al.: Ten to fifteen-year follow-up after total hip arthroplasty with a tapered cobalt-chromium femoral component (tri-lock) inserted without cement. J Bone Joint Surg Am 84-A(12): 2140-2144, 2002.

    

    

2. Burston BJ, Barnett AJ, Amirfeyz R, et al.: Clinical and radiological results of the collarless polished tapered stem at 15 years follow-up. J Bone Joint Surg Br 94(7): 889-894, 2012.

    

    

3. Keisu KS, Orozco F, Sharkey PF, et al.: Primary cementless total hip arthroplasty in octogenarians. Two to eleven-year follow-up. J Bone Joint Surg Am 83-A(3): 359-363, 2001.

    

    

4. Lehman DE, Capello WN, Feinberg JR: Total hip arthroplasty without cement in obese patients. A minimum two-year clinical and radiographic follow-up study. J Bone Joint Surg Am 76(6): 854-862, 1994.

    

    

5. Parvizi J, Keisu KS, Hozack WJ, et al.: Primary total hip arthroplasty with an uncemented femoral component: a longterm study of the Taperloc stem. J Arthroplasty 19(2): 151-156, 2004.

    

    

6. Reitman RD, Emerson R, Higgins L, et al.: Thirteen year results of total hip arthroplasty using a tapered titanium femoral component inserted without cement in patients with type C bone. J Arthroplasty 18(7 Suppl 1): 116-121, 2003.

    

    

7. Streit MR, Innmann MM, Merle C, et al.: Long-term (20- to 25-year) results of an uncemented tapered titanium femoral component and factors affecting survivorship. Clin Orthop Relat Res 471(10): 3262-3269, 2013.

    

    

8. Takenaga RK, Callaghan JJ, Bedard NA, et al.: Cementless total hip arthroplasty in patients fifty years of

   age or younger: a minimum ten-year follow-up. J Bone Joint Surg Am 94(23): 2153-2159, 2012.

    

    

9. Bourne RB, Rorabeck CH: Porous coated femoral fixation: the long and short of it! Orthopedics 26(9): 911-912, 2003.

    

    

10. Burkart BC, Bourne RB, Rorabeck CH, et al.: Thigh pain in cementless total hip arthroplasty. A comparison of two systems at 2 years' follow-up. Orthop Clin North Am 24(4): 645-653, 1993.

     

     

11. Gracia L, Ibarz E, Puértolas S, et al.: Study of bone remodeling of two models of femoral cementless stems by means of DEXA and finite elements. Biomed Eng Online 9: 22, 2010.

     

     

12. Della Valle AG, Padgett DE, Salvati EA: Preoperative planning for primary total hip arthroplasty. J Am Acad Orthop Surg 13(7): 455-462, 2005.

     

     

13. Knight JL, Atwater RD: Preoperative planning for total hip arthroplasty. Quantitating its utility and precision. J Arthroplasty (7 Suppl): 403-409, 1992.

     

     

14. Unnanuntana A, Wagner D, Goodman SB: The accuracy of preoperative templating in cementless total hip arthroplasty. J Arthroplasty 24(2): 180-186, 2009.

     

     

15. Woolson ST, Hartford JM, Sawyer A: Results of a method of leg-length equalization for patients undergoing primary total hip replacement. J Arthroplasty 14(2): 159-164, 1999.

     

     

16. Tripuraneni KR, Archibeck MJ, Junick DW, et al.: Common errors in the execution of preoperative templating for primary total hip arthroplasty. J Arthroplasty 25(8): 1235-1239, 2010.

     

     

17. Sharkey PF, Albert TJ, Hume EL, et al.: Initial stability of a collarless wedge-shaped prosthesis in the femoral canal. Semin Arthroplasty 1(1): 87-90, 1990.

     

     

18. Peak EL, Parvizi J, Ciminiello M, et al.: The role of patient restrictions in reducing the prevalence of early dislocation following total hip arthroplasty. A randomized, prospective study. J Bone Joint Surg Am 87(2): 247-253, 2005.

     

     

19. Schwartz JT, Jr., Mayer JG, Engh CA: Femoral fracture during non-cemented total hip arthroplasty. J Bone Joint Surg Am 71(8): 1135-1142, 1989.

     

     

20. Davidson D, Pike J, Garbuz D, et al.: Intraoperative periprosthetic fractures during total hip arthroplasty. Evaluation and management. J Bone Joint Surg Am 90(9): 2000-2012, 2008.

     

     

21. Sharkey PF, Wolf LR, Hume EL, et al.: Insertional femoral fracture: a biomechanical study of femoral component stability. Semin Arthroplasty 1(1): 91-94, 1990.

     

     

22. Parvizi J, Rapuri VR, Purtill JJ, et al.: Treatment protocol for proximal femoral periprosthetic fractures. J Bone Joint Surg Am 86(A Suppl 2): 8-16, 2004.